1. Field of the Invention
Aspects of the present invention relate to a proton conductive electrolyte, a method of preparing the same, an electrode for a fuel cell, a method of manufacturing the same, and a fuel cell using the proton conductive electrolyte and/or the electrode, and more particularly, to a proton conductive electrolyte suitable for high temperature fuel cells, which remains stable at a high temperature, an electrode that remains stable at a high temperature, and a catalyst and carbon paper used as a support of the electrode are bound to each other with a greatly improved binding force, methods of preparing the proton conductive electrolyte and the electrode, and a fuel cell using the proton conductive electrolyte and/or the electrode.
2. Description of the Related Art
Conventionally, it is known that an ionic conductor is a substance where ions move when a voltage is applied. Ionic conductors are used as electrochemical devices, such as fuel cells, electrochemical sensors, or the like.
For example, in terms of energy generating efficiency, system efficiency, long-term durability of forming members, fuel cells require a proton conductor that exhibits reliable, stable proton conductivity at an operating temperature of 100 to 300° C. under non-humidified conditions or low-humidified conditions with a relative humidity of 50% or less for a long time.
Solid polymer-type fuel cells that comply with this requirement have been developed. For example, a solid polymer-type fuel cell that includes an electrolyte membrane formed of a perfluorocarbonsulfonic has been developed. However, the solid polymer-type fuel cell that includes an electrolyte membrane formed of a perfluorocarbonsulfonic acid cannot sufficiently operate at an operating temperature of 100 to 300° C. in a relative humidity of 50% or less.
Furthermore, there is a fuel cell that includes an electrolyte membrane using a substance that triggers a proton conductivity, a fuel cell that uses a silica diffusion membrane, a fuel cell that uses an inorganic-organic composite membrane, a fuel cell that uses a phosphoric acid-doped graft membrane, and a fuel cell that uses an ionic liquid composite membrane.
In addition, a solid polymer electrolyte membrane formed of polybenzimidazole which is doped with a strong acid, such as a phosphoric acid or the like, is disclosed (in U.S. Pat. No. 5,525,436.)
However, such solid polymer electrolyte membranes described above cannot stably operate for a long time at high temperatures. In particular, long term stability is insufficient at a high operation temperature of 100 to 300° C. under non-humidified conditions or in a relative humidity of 50% or less.
As an example of such a proton conductor, a fuel cell using a perfluorocarbonsulfonic acid or polybenzimidazole (PBI)/polyvinylidenefluoride (PVDF) as an electrode binder is disclosed.
A fuel cell using a perfluorocarbonsulfonic acid as an electrode binder has large mechanical strength, excellent chemical stability, and high ionic conductivity. However, when the fuel cell operates at 80° C. or higher, it loses water and thus cannot be used any more. As a result, when perfluorocarbonsulfonic acid is used as a proton conductor, advantages that can be obtained when a fuel cell operates at high temperatures cannot be obtained. That is, at an operation temperature of 100-300° C. and in a relative humidity of 50% or less, an adequate performance cannot be obtained.
On the other hand, when a fuel cell uses polybenzimidazole (PBI)/polyvinylidenefluoride (PVDF) as an electrode binder, oxygen transmittance thereof is low.
In addition, the fuel cells described above can experience a flooding phenomenon when operating, due to an excessive impregnation with a phosphoric acid, swelling to a substantial degree when operating at high temperatures and thus such fuel cells can undergo partial failure.